1. Field of the Invention
The present invention relates to a magneto-resistance effect element which is configured such that a current is flowed in the direction perpendicular to the film surface thereof. The present invention also relates to a magnetic head, a magnetic recording/reproducing device and a magnetic memory which utilize the magneto-resistance effect element according to the present invention.
2. Description of the Related Art
Recently, the performance of a magnetic device, particularly such as a magnetic head is enhanced by means of Giant Magneto-Resistance Effect (GMR) made of a multilayered magnetic structure. Particularly, since a spin valve film (SV film) can exhibit a larger GMR effect, the SV film has developed the magnetic device such as a magnetic head and MRAM (Magnetic Random Access Memory).
The “spin valve” film has such a structure as sandwiching a non-magnetic metal spacer layer between two ferromagnetic layers and is configured such that the magnetization of one ferromagnetic layer (often called as a “pinning layer” or “fixed magnetization layer) is fixed by the magnetization of an anti-ferromagnetic layer and the magnetization of the other ferromagnetic layer (often called as a “free layer” or “free magnetization layer”) is rotated in accordance with an external magnetic field. With the spin valve film, the large MR effect can be obtained by the variation of the relative angle in magnetization between the pinned layer and the free layer.
A conventional spin valve film is employed for a CIP (Current In plane)-GMR element. In the CIP-GMR element, a sense current is flowed to the SV film in the direction parallel to the film surface thereof. Recently, attention is paid to a CPP (Current Perpendicular to Plane)-GMR element and a TMR (Tunneling Magneto Resistance) element because the CPP-GMR element and the TMR element can exhibit the respective large MR effect in comparison with the CIP element. In the CPP-GMR element and the TMR element, a sense current is flowed to the SV film in the direction almost perpendicular to the film surface thereof.
Recently, it was confirmed that a large MR effect with high MR-ratio can be obtained from the minute coupling of Ni wires (Reference 1).
Then, the minute magnetic coupling is formed three-dimensionally so as to realize a magneto-resistance effect element with high MR ratio (Reference 2). In this case, the three-dimensional minute magnetic coupling is carried out by means of EB (Electron beam) irradiation, FIB (Focused Ion beam) irradiation or AFM (Atomic Force Microscope).    [Reference 1] Phys. Rev. Lett. 82 2923 (1999)    [Reference 2] JP-A 2003-204095 (KOKAI)
It is considered that the MR effect as described above is originated from the rapid variation in magnetization at the minute magnetic coupling point. Namely, if the magnetic domain to be formed at the minute magnetic coupling point is narrowed, the large MR effect can be obtained. The magnetic domain can be indirectly narrowed by decreasing the size (diameter) of the minute magnetic coupling point (the size (diameter) of the ferromagnetic metallic portion of the complex spacer layer). However, too small size of the minute magnetic coupling point may increase the resistance thereof excessively.
On the other hand, if the size of the minute magnetic coupling point is enlarged, the resistance of the minute magnetic coupling point can be reduced, but too large size of the minute magnetic coupling point may strengthen the magnetic coupling between the pinned layer and the free layer via the minute magnetic coupling so as to increase the interlayer-coupling. The increase of the interlayer-coupling causes undesirably the shift of the operating point toward the higher magnetic field at the magnetic head containing the minute magnetic coupling.